Turbo Charged Air Temps
Discussion
I've recently put together, with the help of a machine shop, a new 2L turbo forged engine. I'm now driving the car with the standard turbo, but I'm starting to think about cooling the charged air in readiness for a bigger turbo. what i'd like to get opinions on is, how cooler does a bigger turbo blow compared to a smaller one. I've not really explained this very well, but is the charged air noticeably cooler with the bigger turbo at the same psi as the smaller one. thanks.
jontysafe said:
Soooo
what engine is it? Not that that has too much bearing.but CR, target power, torque characteristics and target, max rpm etc. Road/track?
You clearly don't know the answer so are just asking unrelated questions for some reason. I would just advise leaving it until someone comes along who knows the answer.what engine is it? Not that that has too much bearing.but CR, target power, torque characteristics and target, max rpm etc. Road/track?
In some respects it's a pointless question.
Simply fit the biggest and best intercooler you can do the car. The car itself is always the biggest limitation as to size/location of any core used even if you had a lot of heat to deal with. Garrett make the best cores.
Although 400hp worth shouldnt be difficult to deal with, by any accounts it is a modest goal.
BW EFR 6258 would do or 6758
Or something along the lines of a Precision 5130
If you really had to use a Garrett, the likes of a GEN2 GTX860R would be better than any of the GT30's
You also dont state which Celica....and whether you currently have, or expect to try and use the OE water based cooler, or will change to a more conventional air to air unit.
Or if you have the older air to air on top of the engine, and wish to retain this location or do things properly with a decent front mount etc.
Simply fit the biggest and best intercooler you can do the car. The car itself is always the biggest limitation as to size/location of any core used even if you had a lot of heat to deal with. Garrett make the best cores.
Although 400hp worth shouldnt be difficult to deal with, by any accounts it is a modest goal.
BW EFR 6258 would do or 6758
Or something along the lines of a Precision 5130
If you really had to use a Garrett, the likes of a GEN2 GTX860R would be better than any of the GT30's
You also dont state which Celica....and whether you currently have, or expect to try and use the OE water based cooler, or will change to a more conventional air to air unit.
Or if you have the older air to air on top of the engine, and wish to retain this location or do things properly with a decent front mount etc.
Edited by stevieturbo on Saturday 19th January 12:02
Perhaps we need to start at the beginning!
Turbos "blow hot" because they compress air, ie they increase charge air density (they do NOT blow air into the engine, quite the opposite in fact)
When air is compressed, work is done on the air ie energy is added to the air from the thing doing the compressing, in this case, the turbocharger compressor wheel.
The temperature increase depends on 3 things:
1) what exactly is being compressed and the Specific Heat Capacity of that substance (air).
2) How much is it compressed (the pressure ratio)
3) How efficiently the compression process works (the compression efficiency)
Now, realistically, for any given compression ratio, 1) and 2) are fixed, because we are compressing air from say 1 bar to 2 bar (absolute)
Therefore what matters is the efficiency of that compression process.
Further up ^^^^ in this thread a poster put up a table of temperatures, for a fixed compression ratio, and it's clear to see, as the compression efficiency falls, the temperature increases, because the air absorbs more work to get to any given compression ratio, and more work is more heat
So, that leads us directly into the next question: How efficient is my compressor?
And the short answer here is "it depends". In fact a centrifugal compressor, such as the one in your turbo has a complex efficiency map, and the efficiency varies hugely with massflow and pressure ratio. This is best described using a "compressor map"
Here's one for a Gt3076:
As you can see, its plotted as a series of lines of fixed efficiency which form "efficiency islands" on the map. In this case, peak efficiency is 77%, but only across a narrow curved island in the centre of the map.
There are plenty of google hits on how to read compressor maps, and how to choose the correct size turbo charger, but you will need to at the least make some reasonable estimates of the airflow characteristics of your engine.
In all cases, remember however that the compressor map is for a turbo under ideal conditions, when in fact, under the bonnet is often far from ideal. This is particularly pertinent to compressor inlet pressure losses, ie the dirty air duct / air box and airfilter / clean air duct. Pressure losses here are twice as bad as downstream (post compressor) losses because the pressure ratio is, well a ratio, ie something divided by something else. for example an increase from 1 bar to 2 bar is a pressure ratio of 2 (2/1 = 2) whereas compression from 0.5 bar (half the original pressure) to 2 bar is a pressure ratio of 4! (2/0.5 = 4).
Presenting the compressor inducer with air at the highest pressure (ie least intake loss), as uniformly as possible (all the air flowing forwards at right angles to the compressor wheel front face), and across the full area (ie an even flow /pressure distrubution across the compressor face) is critical in ensuring the INSTALLED efficiency is as high as possible.
Turbos "blow hot" because they compress air, ie they increase charge air density (they do NOT blow air into the engine, quite the opposite in fact)
When air is compressed, work is done on the air ie energy is added to the air from the thing doing the compressing, in this case, the turbocharger compressor wheel.
The temperature increase depends on 3 things:
1) what exactly is being compressed and the Specific Heat Capacity of that substance (air).
2) How much is it compressed (the pressure ratio)
3) How efficiently the compression process works (the compression efficiency)
Now, realistically, for any given compression ratio, 1) and 2) are fixed, because we are compressing air from say 1 bar to 2 bar (absolute)
Therefore what matters is the efficiency of that compression process.
Further up ^^^^ in this thread a poster put up a table of temperatures, for a fixed compression ratio, and it's clear to see, as the compression efficiency falls, the temperature increases, because the air absorbs more work to get to any given compression ratio, and more work is more heat
So, that leads us directly into the next question: How efficient is my compressor?
And the short answer here is "it depends". In fact a centrifugal compressor, such as the one in your turbo has a complex efficiency map, and the efficiency varies hugely with massflow and pressure ratio. This is best described using a "compressor map"
Here's one for a Gt3076:
As you can see, its plotted as a series of lines of fixed efficiency which form "efficiency islands" on the map. In this case, peak efficiency is 77%, but only across a narrow curved island in the centre of the map.
There are plenty of google hits on how to read compressor maps, and how to choose the correct size turbo charger, but you will need to at the least make some reasonable estimates of the airflow characteristics of your engine.
In all cases, remember however that the compressor map is for a turbo under ideal conditions, when in fact, under the bonnet is often far from ideal. This is particularly pertinent to compressor inlet pressure losses, ie the dirty air duct / air box and airfilter / clean air duct. Pressure losses here are twice as bad as downstream (post compressor) losses because the pressure ratio is, well a ratio, ie something divided by something else. for example an increase from 1 bar to 2 bar is a pressure ratio of 2 (2/1 = 2) whereas compression from 0.5 bar (half the original pressure) to 2 bar is a pressure ratio of 4! (2/0.5 = 4).
Presenting the compressor inducer with air at the highest pressure (ie least intake loss), as uniformly as possible (all the air flowing forwards at right angles to the compressor wheel front face), and across the full area (ie an even flow /pressure distrubution across the compressor face) is critical in ensuring the INSTALLED efficiency is as high as possible.
Edited by anonymous-user on Saturday 19th January 13:52
Max_Torque
Nice write up
hotrat
I have not looked in sometime. But some of the turbo companies use to have calculator on their web sites. This can be a complex subject. You can produce more HP with less boost if the compressed air temperature is much less than the higher boost. All of this is shown in just one number called "Density Ratio".
Stan
Nice write up
hotrat
I have not looked in sometime. But some of the turbo companies use to have calculator on their web sites. This can be a complex subject. You can produce more HP with less boost if the compressed air temperature is much less than the higher boost. All of this is shown in just one number called "Density Ratio".
Stan
227bhp said:
Max_Torque said:
Lots of blether
What's the answer to the question though?but it summarises to:
"the best turbo is the one with the highest efficiency at the Pressure ratio and Mass flow that matches the engine in question"
I have explained the science in terms a GSCE level child could easily understand. It's up to the OP now to decide if they can be bothered to try to learn and understand and apply what i have told them.
Ok, I have a turbo engine that uses a charge cooler setup. My tuner guy tells me that the charge cooler setup is now struggling to cope with the inlet temps from my small standard turbo, It's maxing out at 1.1bar, 285hp. As I'm about to fit a bigger turbo, it got me thinking, would it blow a little bit cooler as it did'int have to work as hard, and allow me to keep the charge cooler setup I already have. I'll find this out myself by trying it.
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